In an ink jet recording method, fine ink drops ejected by a wide variety of mechanisms are made to adhere to a recording material, such as paper, thereby recording pictures and letters thereon. Since the ink jet recording method is a noiseless and high-speed recording method, enables easy formation of full color images and requires no developing and fixing operations, the range of its use has shown a rapid rate of increase. Further, a multicolor ink jet recording method enables the formation of color images which can stand comparison with multicolor prints obtained by a plate-making process or color photography, and that at a lower price than color photography so far as there is no need of making a number of copies. Thus, the ink jet recording method is being widely utilized in the field of full-color image recording also.
Much effort to utilize woodfree paper and coated paper, which are generally used in graphic arts or as writing paper, as the recording paper for ink jet recording have been made from the apparatus and ink composition sides. As a result thereof, ink jet recording apparatus has undergone various improvements in performances, and thereby high-speed, high definition or/and full-color recording has been realized and the range of its use is being increased. However, such advances in the recording apparatus have come to require higher levels of characteristics for the recording paper side.
More specifically, the ink jet recording paper is required to have properties of (i) ensuring a high dot density and a bright-and-vivid tone (excellent coloring) in the ink dot images recorded thereon, (ii) enabling high-speed drying of ink to cause neither running nor bleeding of the ink even when ink dots are overlapped, and (iii) enabling a moderate diffusion of ink dots in the horizontal direction to ensure a smooth and clear circumference in the ink dots adhering thereto. Further, it is required as an important factor in forming images of high quality that the recording material causes only a slight decrease in gloss by recording.
A cause of decrease in gloss by recording is as follows: The ink-receiving layer of a recording material absorbs ink upon ink jet recording, and the resin and the pigment contained therein are dissolved in the ink or get swollen as they absorb the ink, thereby destroying the surface of the recording material.
It has so far been required for an ink jet recording paper to meet two essential conditions that the recording material should ensure (1) excellent image quality and (2) no decrease in gloss due to ink jet recording. For the purpose of obtaining a substitute for color photographic paper or conferring a high-grade feeling on the printed (recorded) images, a new requirement that the gloss itself which the ink jet recording paper has after recording should be higher than usual has recently been added to the aforementioned ones.
With the intention of solving those problems, some proposals as described briefly below have hitherto been made.
For instance, as means for providing excellent image quality, there has been disclosed the ink jet recording paper prepared by applying a coating color for surface conversion to a low sized raw paper (Japanese Tokkai Sho 52-53012, wherein the term "Tokkai" as used herein means an "unexamined published patent application") and the ink jet recording paper prepared by impregnating a sheet containing therein urea-formaldehyde resin particles with a water-soluble high polymer (Japanese Tokkai sho 53-49113). These ink jet recording papers of general paper type can absorb ink quickly, but it has disadvantage in that the circumferences of ink dots put thereon are liable to be blurred and the density thereof becomes low.
In addition, the ink jet recording paper having an ink absorbing layer coated on the support surface is disclosed in Japanese Tokkai Sho 55-5830, and the case wherein the pigment used in the layer coated on the support surface is a silica powder is disclosed in Japanese Tokkai Sho 55-51581. These ink jet recording papers of coated paper type have improvements in the diameter, the shape and the density of ink dots and the reproduction of color tone over ink jet recording papers of general paper type.
The ink applied to those recording papers is generally water-base ink using water-soluble dyes. Therefore, when the images formed on the recording papers are exposed to water or the like, the dyes are dissolved again to ooze out to the paper surface; as a result, the value as a recorded matter is markedly lowered. In other words, such recording papers have a problem of being poor in water resistance.
On the other hand, the case where the ink receiving layer contains a large amount of water-soluble resin has a defect that the swelling or the dissolution of the resin occurs upon contact with ink to lower the gloss in the printed area (the area which is in contact with ink).
For the purpose of mitigating those drawbacks, the improvement in water resistance or the like by the incorporation of porous cationic hydrated aluminum oxide has been proposed in Japanese Tokko Hei 3-24906 (Registration No. 1735506), wherein the term "Tokko" as used herein means an "examined patent publication". In this proposal, attention is focused on the porosity of hydrated aluminum oxide. More specifically, liquid substances, such as ink and water, can get into pores of the hydrated aluminum oxide; as a result, it becomes very difficult for ink to cause the swelling or the dissolution of the ink receiving layer. Thus, the decrease in gloss due to recording can be reduced.
Although this proposal enables an ink jet recording paper to fulfil two requirements, namely (i) excellent image quality and (ii) no decrease in gloss by ink jet recording, it is still unsuccessful in ensuring sufficient gloss in the ink jet recording paper after recording.
As means to prepare an ink jet recording paper having high gloss enough to ensure sufficient gloss after recording, there are known (1) a method in which paper is passed between heat- and pressure-applied roll nips, such as a method of using a super calender, and (2) a method in which an ink receiving layer in a wet state is brought into contact with a heated specular surface under pressure and then dried (which is referred to as a "cast coating method" in the arts of preparing coated papers), as disclosed in Japanese Tokkai Hei 6-79967.
However, the application of the former method to the ink jet recording paper having an ink receiving layer formed by directly coating a support with a porous inorganic composition as described in Japanese Tokko Hei 3-24906 (e.g., alumina and silica) enables the recording paper to have a highly glossy surface, but causes the collapse of pores formed by the use of the porous inorganic composition to render the coated layer itself hard. Thus, the ink absorbency is lowered to fail in achieving excellent image quality.
In the application of the latter method (cast coating method), on the other hand, the coating color provided on a support to form an ink receiving layer has many restrictions as to viscosity, solid concentration and so on because of the properties of an inorganic composition used therein, such as alumina sol, and it is difficult to thicken the ink receiving layer by increasing the coverage rate. This is because when the concentration of an inorganic composition, such as alumina sol, is heightened the coating color has an excessively increased viscosity to result in a lack of coating suitability. In other words, only an ink receiving layer having small thickness can be formed in this case. Therefore, sufficient ink absorbency cannot be achieved and the images of good quality cannot be formed.
Under these circumstances, the Inventors continued researches into new methods, other than super calendering and cast coating methods, for producing an ink jet recording paper which not only causes no decrease in gloss upon recording but also ensures excellent image quality and high gloss after recording and, as disclosed in Japanese Tokkai Hei 8-164668, developed a transferring technique for producing an ink jet recording paper having a high surface gloss. However, this transferring technique is still unsatisfactory. This is because the transferring technique cited above has a disadvantage in that, since the ink receiving layer provided on the support of a transfer material is transferred and bonded directly to a base paper used as the substrate of an ink jet recording paper to be produced, the texture and the whiteness of the base paper are apt to be reflected in the surface of the ink jet recording paper as the final product and, in other words, the surface properties of the final product are susceptible to the properties of a base paper used as the substrate onto which an ink receiving layer is transferred. Further, the ink receiving layer comprising a porous inorganic composition is required to have a thickness of the order of 30 microns for acquiring the desired ink absorbency. However, the coating color for forming such a thick layer comes expensive on account of a high price of the inorganic composition and further, it is difficult to control the coating color upon storage so as to retain a high concentration enough to form such a thick layer. In addition, the transferring technique cited above is inferior in production efficiency since it takes too much time to dry the layer containing a porous inorganic composition in high proportion.